Author:

Dmitry Ruzmetov(Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD, USA)

The ability to measure the morphological, chemical, and transport
characteristics with nanoscale resolution in electrochemical energy storage
devices is critical for understanding the complex interfacial reactions and
phase transformation that accompany cycling of secondary batteries. In this
talk I will describe the use of an all-nanowire Li ion battery for \textit{in situ}
characterization of charge and discharge reactions. The nanowire batteries
(NWBs) consist of a metalized core, a LiCoO$_{2}$ cathode, LiPON solid
electrolyte, and a thin film Si anode. Measuring several micrometers in
length and several hundred nanometers in diameter, the NWBs can be readily
imaged and analyzed in transmission electron microscopes (TEM, STEM). We use
focused ion beam milling and electron beam induced deposition to separate
the cathode and anode and fabricate Pt contacts to a NWB. \textit{In situ} electrical
cycling of NWBs in TEM reveals that the most of the structural changes due
to cycling happens in the electrolyte layer especially near the
cathode/electrolyte interface. Electrical response from a single NWB was
measured in the sub-pA range. For NWBs with the thinnest electrolyte,
approximately 100 nm, we observe rapid self-discharge, along with void
formation at the electrode/electrolyte interface, indicating electrical and
chemical breakdown. The analysis of the NWB's electrical characteristics
reveals space-charge limited electronic conduction, which effectively shorts
the anode and cathode electrodes. When the electrolyte thickness is
increased, the self-discharge rate is reduced substantially and the NWBs
maintain a potential above 2 V. Our study illustrates that at reduced
dimensions the increase in the electric field can lead to large electronic
current in the electrolyte effectively shorting the battery even when the
electrolyte layer is uniform and pinhole free. The scaling of this
phenomenon provides useful guidelines for design of 3D Li ion batteries.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.W2.4